1. Field of the Art
The present invention relates to an improvement of a disinfecting solution for contact lenses. In particular, the invention is concerned with such a disinfecting solution which exhibits an excellent disinfecting or preservative effect while assuring significantly enhanced safety to the eyes of the lens wearer. Further, the present invention relates to the disinfecting solution which permits the contact lenses to be directly worn on the eyes of the lens wearer, without a need of rinsing of the lenses after they are treated with the disinfecting solution.
2. Discussion of the Related Art
Generally, contact lenses are classified into hydrophobic contact lenses and hydrophilic or hydrated contact lenses, or hard contact lenses and soft contact lenses. These contact lenses may be soiled with deposits such as protein and lipid during wearing of the contact lenses on the eyes, which deposits derive from tear fluid and lipid of the eyes. These deposits adhering to the contact lenses deteriorate the wearing comfort of the contact lenses as felt by the lens wearer, lower the eyesight of the lens wearer, and cause various troubles with the eyes such as hyperemia of the conjunctiva. In view of these problems, the contact lenses which have been removed from the eyes need to be cleaned for safe and comfortable wearing thereof.
Besides the cleaning treatment described above, the contact lenses which have been removed from the eyes need to be disinfected, and then stored in a suitable storing liquid for the purpose of preventing proliferation of microorganisms such as bacteria and molds on the lens surfaces during storage thereof. The procedure for treating the contact lenses such as cleaning, disinfecting and storing is indispensable for safe wearing of the contact lenses on the eyes of the lens user.
The procedure for treating the contact lenses is, however, considerably cumbersome, requiring several kinds of liquid agents such as a cleaning solution, a disinfecting solution, and a storing solution. Accordingly, it is troublesome and costly for the contact lens users to treat and maintain the contact lenses.
For solving the above problem, various multi-purpose contact lens liquid agents are commercially available at home and abroad. These multi-purpose liquid agents are obtained by adding, to a storing solution, a surface active agent and a disinfectant. The contact lenses can be cleaned, rinsed, disinfected, and stored by using such a single liquid agent.
Although various compounds are conventionally proposed as the disinfectant to be included in those liquid agents, these compounds need to be used in relatively high concentrations for permitting the liquid agents to exhibit a practically sufficient disinfecting effect. For instance, biguanide derivatives whose typical example is polyhexamethylene biguanide (PHMB) have been recently attracting attentions as the disinfectant. The biguanide derivatives are one example of a high-molecular organic disinfectant containing nitrogen groups (organic nitrogen disinfectant), and have a superior disinfecting property as compared to the other disinfectants. A recent study, however, reveals that the biguanide derivatives alone do not provide a sufficiently high disinfecting or preservative effect. Accordingly, for assuring a practically useful disinfecting effect, it is necessary to increase the amount of the biguanide derivatives to be included in the contact lens liquid agents. The biguanide derivatives if used in high concentrations, however, are toxic to the eyes, and irritate the mucous membranes of the eyes to cause inflammation, giving rise to a problem of insufficient safety. In view of this, various studies have been made to provide a contact lens liquid agent capable of exhibiting a higher disinfecting effect while reducing the required amount of the biguanide derivatives.
For instance, JP-A-6-321715 discloses a contact lens disinfecting and storing solution which uses the biguanide derivative together with a boric acid buffer. The disclosed solution has a low degree of toxicity to the eyes while having a high level of antimicrobial activity. JP-A-6-504044 discloses a contact lens disinfecting composition which includes the biguanide derivative in combination with a tris buffer. The disclosed composition has an excellent disinfecting property and gives substantially no irritation to the eyes. Both of the disclosed solution and composition, however, are not considered to have satisfactorily high disinfecting efficacy.
JP-A-52-110055 discloses a contact lens storing solution obtained by dissolving in an organic alcohol or a non-aqueous solvent, a disinfectant formed of an ene-diol compound, in combination with a catalytic metal compound (catalyst). The proposed storing solution suffers from problems such as a low disinfecting capability due to the use of the ene-diol compound as the disinfecting component, and insufficient safety resulting from the use of the metallic catalyst.
JP-A-8-224288 and JP-A-9-38180 disclose a method of simultaneously cleaning and disinfecting contact lenses, by using a cleaning and disinfecting solution which contains an effective amount of protease, a predetermined amount of glycerin, water, and 60-80 w/v % or 15-60 w/v % of propylene glycol. In the disclosed treating solution, the concentration of propylene glycol is considerably high, undesirably increasing the osmotic pressure of the treating solution, whereby the material of the contact lenses may be adversely affected. Since the treating solution contains the protease, the contact lenses which have been treated with the treating solution need to be rinsed with a suitable rinsing solution before the contact lenses are worn on the eyes of the lens user. If the contact lenses are worn on the eyes without being rinsed, the treating solution remaining on the contact lenses may irritate the eyes.
JP-A-6-194610 discloses a method of cleaning, storing and disinfecting contact lenses, by using a treating solution which contains an effective amount of Bacillus-derived serine protease and a metal chelating agent, wherein the serine protease is stabilized by a boric acid and/or borax. The publication suggests inclusion of 0.5-2 w/v % of polyhydric alcohol in the treating solution, merely for improving the stability of the enzyme (serine protease) in the treating solution. Since the disclosed treating solution contains the serine protease (proteolytic enzyme), the contact lenses which have been treated with the treating solution need to be sufficiently rinsed with a rinsing solution before the contact lenses are worn on the eyes of the lens wearer. When the contact lenses are worn on the eyes without being rinsed, the treating solution remaining on the contact lenses may cause various troubles with the eyes such as keratitis and conjunctivitis.